Fainting: What Makes You Faint?

You're Dehydrated

Dehydration can happen if you don't drink enough or you lose too much fluid. Then your blood pressure drops and your nervous system can't control it well, which could make you faint. That's why it's a good idea to get plenty of water, especially when it's hot outside. If your pee isn't clear, you may need a bit more to drink.

Arrhythmia

It means your heart has an irregular beat. That sometimes slows the flow and amount of blood that gets to your brain, which can make you pass out. It may be the first or only obvious symptom of the problem. See your doctor right away if you suspect arrhythmia because it could be a sign of a serious heart problem that needs treatment.

Cyanotic Breath-Holding

It happens mostly in kids between ages 6 months and 5 years. They cry hard enough to cut off oxygen and trigger an automatic response that makes them faint. They may turn blue, pass out for about a minute, and seem groggy afterward. They don't do it on purpose. It's a reflex they can't control. Though it's scary to see at first, it's nothing to worry about and might even happen repeatedly.

Pallid Breath-Holding

This one also happens mainly in young kids. A sudden fright or pain causes the heart to stop for a few seconds. With no sound, a child might open his mouth before turning very pale and passing out for about a minute. Pallid breath-holding sometimes happens after your child gets hurt. It's not the injury itself that causes this automatic response, but the shock of it. It should go away by age 5.

Low Blood Sugar

The medical term is hypoglycemia. It may make you dizzy, shaky, tired, confused, and blur your vision. You can usually fix the problem if you get a few grams of carbs from juice or candy. Otherwise, you could pass out. If that happens, you need medicine called glucagon to help your body release more sugar.

Diabetes

High blood sugar from diabetes can damage the nerves in your body that help keep your blood pressure steady. That could lead to unusually low blood pressure that makes you pass out.

Medicine

Some medications, like high blood pressure drugs and antidepressants, affect the way your heart and blood vessels act when you stand. This can drop your blood pressure and make you pass out. Insulin used to lower blood sugar when you have diabetes might cause hypoglycemia that also leads to fainting. In older people, different drugs sometimes combine with illness and the situation you're in -- like standing in a hot room --to make you faint.

Seizure

It's a sudden change in the brain's normal electrical signals. Some symptoms, like eyes rolling back and jerking movements, may be similar to breath-holding. The difference is seizures make you unconscious for minutes, not seconds, and might make you lose control of your bladder. And you could see flashes of light or get unusual smells or tastes with no obvious source. See your doctor if you suspect a seizure.

Standing Up

If you faint when you rise, you could have a condition called postural orthostatic tachycardia syndrome (POTS). It increases your pulse too much when you stand or sit up. You might feel sick, dizzy, shaky, or sweaty, and your heart may skip a beat. And you could pass out. It can help to drink plenty of fluids, limit caffeine and alcohol, and try to get up more slowly. Your doctor may suggest medicine to treat it.

Heart Problems

Damaged heart muscle, blocked or narrowed blood vessels (coronary heart disease), and other kinds of ticker trouble can stop enough blood loaded with oxygen from getting to your brain. When it makes you pass out, it's called cardiac syncope. It may happen without warning, sometimes repeatedly over a period of weeks. See your doctor right away if you suspect this or also have chest pain, arrhythmia, fatigue, or other symptoms.

Shock

The technical term for this is vasovagal syncope. Your body overreacts to the sight of blood, sudden intense emotion, fear of injury, or something else that jars you. Your heart rate slows as blood vessels widen and blood pools in your legs, away from your brain. You may be cold, clammy, pale, and nauseated right before it happens. If you feel like you might faint, lie down and raise your legs.

Hyperventilation

You feel like you can't get enough air, so you start to breathe in more quickly. Though it's unclear why, this makes blood vessels around your brain shrink, which limits oxygen and makes you lightheaded and possibly faint. Fear, rather than a physical problem, usually causes it, though you can bring it on if you hold your breath. Your hands, feet, and mouth might also tingle.

Coughing

Especially if it's deep and you can't stop, it might prevent your blood from getting enough oxygen, which could make you faint. It's more common in babies with pertussis, but it can happen to anyone. Asthma, which makes it harder to breathe, may have the same effect. Get to a hospital right away if you have a serious asthma attack or pass out from coughing.

Drinking Alcohol

It causes your blood vessels to expand, which can lead to a drop in your blood pressure. You can pass out when you drink so much that you reach a dangerously high blood alcohol concentration.

Your Collar's Too Tight

Carotid sinus syncope, or "tight-collar syndrome," happens when something pushes on nerves at a wide part of your carotid artery in your neck. This interferes with blood flow to the brain and makes you faint. It happens quickly and without other symptoms like nausea, paleness, and sweating. In some cases, if it hasn't happened before, it may be a sign of narrowed arteries that need treatment.

THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for general informational purposes only and does not address individual circumstances. It is not a substitute for professional medical advice, diagnosis or treatment and should not be relied on to make decisions about your health. Never ignore professional medical advice in seeking treatment because of something you have read on the MedicineNet Site. If you think you may have a medical emergency, immediately call your doctor or dial 911.